Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx> writes: > On Wed, Nov 16, 2022 at 07:03:49PM +0000, Alex Bennée wrote: >> >> Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx> writes: >> >> > On Tue, Nov 15, 2022 at 04:56:12PM +0000, Alex Bennée wrote: >> >> >> >> Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx> writes: >> >> >> >> > This new KVM exit allows userspace to handle memory-related errors. It >> >> > indicates an error happens in KVM at guest memory range [gpa, gpa+size). >> >> > The flags includes additional information for userspace to handle the >> >> > error. Currently bit 0 is defined as 'private memory' where '1' >> >> > indicates error happens due to private memory access and '0' indicates >> >> > error happens due to shared memory access. >> >> > >> >> > When private memory is enabled, this new exit will be used for KVM to >> >> > exit to userspace for shared <-> private memory conversion in memory >> >> > encryption usage. In such usage, typically there are two kind of memory >> >> > conversions: >> >> > - explicit conversion: happens when guest explicitly calls into KVM >> >> > to map a range (as private or shared), KVM then exits to userspace >> >> > to perform the map/unmap operations. >> >> > - implicit conversion: happens in KVM page fault handler where KVM >> >> > exits to userspace for an implicit conversion when the page is in a >> >> > different state than requested (private or shared). >> >> > >> >> > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx> >> >> > Co-developed-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx> >> >> > Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx> >> >> > Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx> >> >> > --- >> >> > Documentation/virt/kvm/api.rst | 23 +++++++++++++++++++++++ >> >> > include/uapi/linux/kvm.h | 9 +++++++++ >> >> > 2 files changed, 32 insertions(+) >> >> > >> >> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst >> >> > index f3fa75649a78..975688912b8c 100644 >> >> > --- a/Documentation/virt/kvm/api.rst >> >> > +++ b/Documentation/virt/kvm/api.rst >> >> > @@ -6537,6 +6537,29 @@ array field represents return values. The userspace should update the return >> >> > values of SBI call before resuming the VCPU. For more details on RISC-V SBI >> >> > spec refer, https://github.com/riscv/riscv-sbi-doc. >> >> > >> >> > +:: >> >> > + >> >> > + /* KVM_EXIT_MEMORY_FAULT */ >> >> > + struct { >> >> > + #define KVM_MEMORY_EXIT_FLAG_PRIVATE (1 << 0) >> >> > + __u32 flags; >> >> > + __u32 padding; >> >> > + __u64 gpa; >> >> > + __u64 size; >> >> > + } memory; >> >> > + >> >> > +If exit reason is KVM_EXIT_MEMORY_FAULT then it indicates that the VCPU has >> >> > +encountered a memory error which is not handled by KVM kernel module and >> >> > +userspace may choose to handle it. The 'flags' field indicates the memory >> >> > +properties of the exit. >> >> > + >> >> > + - KVM_MEMORY_EXIT_FLAG_PRIVATE - indicates the memory error is caused by >> >> > + private memory access when the bit is set. Otherwise the memory error is >> >> > + caused by shared memory access when the bit is clear. >> >> >> >> What does a shared memory access failure entail? >> > >> > In the context of confidential computing usages, guest can issue a >> > shared memory access while the memory is actually private from the host >> > point of view. This exit with bit 0 cleared gives userspace a chance to >> > convert the private memory to shared memory on host. >> >> I think this should be explicit rather than implied by the absence of >> another flag. Sean suggested you might want flags for RWX failures so >> maybe something like: >> >> KVM_MEMORY_EXIT_SHARED_FLAG_READ (1 << 0) >> KVM_MEMORY_EXIT_SHARED_FLAG_WRITE (1 << 1) >> KVM_MEMORY_EXIT_SHARED_FLAG_EXECUTE (1 << 2) >> KVM_MEMORY_EXIT_FLAG_PRIVATE (1 << 3) > > Yes, but I would not add 'SHARED' to RWX, they are not share memory > specific, private memory can also set them once introduced. OK so how about: KVM_MEMORY_EXIT_FLAG_READ (1 << 0) KVM_MEMORY_EXIT_FLAG_WRITE (1 << 1) KVM_MEMORY_EXIT_FLAG_EXECUTE (1 << 2) KVM_MEMORY_EXIT_FLAG_SHARED (1 << 3) KVM_MEMORY_EXIT_FLAG_PRIVATE (1 << 4) > > Thanks, > Chao >> >> which would allow you to signal the various failure modes of the shared >> region, or that you had accessed private memory. >> >> > >> >> >> >> If you envision any other failure modes it might be worth making it >> >> explicit with additional flags. >> > >> > Sean mentioned some more usages[1][]2] other than the memory conversion >> > for confidential usage. But I would leave those flags being added in the >> > future after those usages being well discussed. >> > >> > [1] https://lkml.kernel.org/r/20200617230052.GB27751@xxxxxxxxxxxxxxx >> > [2] https://lore.kernel.org/all/YKxJLcg%2FWomPE422@xxxxxxxxxx >> > >> >> I also wonder if a bitmask makes sense if >> >> there can only be one reason for a failure? Maybe all that is needed is >> >> a reason enum? >> > >> > Tough we only have one reason right now but we still want to leave room >> > for future extension. Enum can express a single value at once well but >> > bitmask makes it possible to express multiple orthogonal flags. >> >> I agree if multiple orthogonal failures can occur at once a bitmask is >> the right choice. >> >> > >> > Chao >> >> >> >> > + >> >> > +'gpa' and 'size' indicate the memory range the error occurs at. The userspace >> >> > +may handle the error and return to KVM to retry the previous memory access. >> >> > + >> >> > :: >> >> > >> >> > /* KVM_EXIT_NOTIFY */ >> >> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h >> >> > index f1ae45c10c94..fa60b032a405 100644 >> >> > --- a/include/uapi/linux/kvm.h >> >> > +++ b/include/uapi/linux/kvm.h >> >> > @@ -300,6 +300,7 @@ struct kvm_xen_exit { >> >> > #define KVM_EXIT_RISCV_SBI 35 >> >> > #define KVM_EXIT_RISCV_CSR 36 >> >> > #define KVM_EXIT_NOTIFY 37 >> >> > +#define KVM_EXIT_MEMORY_FAULT 38 >> >> > >> >> > /* For KVM_EXIT_INTERNAL_ERROR */ >> >> > /* Emulate instruction failed. */ >> >> > @@ -538,6 +539,14 @@ struct kvm_run { >> >> > #define KVM_NOTIFY_CONTEXT_INVALID (1 << 0) >> >> > __u32 flags; >> >> > } notify; >> >> > + /* KVM_EXIT_MEMORY_FAULT */ >> >> > + struct { >> >> > +#define KVM_MEMORY_EXIT_FLAG_PRIVATE (1 << 0) >> >> > + __u32 flags; >> >> > + __u32 padding; >> >> > + __u64 gpa; >> >> > + __u64 size; >> >> > + } memory; >> >> > /* Fix the size of the union. */ >> >> > char padding[256]; >> >> > }; >> >> >> >> >> >> -- >> >> Alex Bennée >> >> >> -- >> Alex Bennée -- Alex Bennée
